Boron trifluoride complex catalysts composed of boron trifluoride and a complexing agent, ligand, are used widely in industrial fields as catalysts for various chemical reactions such as alkylation, isomerization, polymerization, decomposition and dehydration. These complex catalysts are utilized in the form of various complexing agents coordinated to boron trifluoride in appropriate ratios for objective reactions.
After the reaction using a boron trifluoride complex catalyst, it is necessary to separate the complex catalyst from the reaction mixture. For this purpose, a method is usually made used of neutralizing the catalyst with an aqueous solution of basic substance such as ammonia or caustic soda, and then washing with water.
Disclosed in U.S. Pat. No. 4,227,027 is another method which comprises adding a polyhydric alcohol having two or more hydroxyl groups to the reaction mixture containing a boron -trifluoride complex catalyst, causing addition reaction of the alcohol with only boron trifluoride in the complex catalyst to remove boron trifluoride, and decomposing the addition product by heating to recover boron trifluoride.
Furthermore, Japanese Laid-Open Patent Publication No. 6-287211 discloses a method of reaction using a boron trifluoride complex catalyst, which comprises heating a reaction mixture to vaporize boron trifluoride gas, contacting the boron trifluoride gas with a complexing agent in excess relative to boron trifluoride to form a new complex, and recycling it into the reactor for reuse.
In these methods, however, the boron trifluoride is separated and recovered solely, so that an additional complexing step is necessary for the reuse of complex catalyst, with the result that a multi-stage process is necessary and the increase of costs is caused. As for the method disclosed in Japanese Laid-Open Patent Publication No. 6-287211, the reaction mixture is heated in coexistence with a boron trifluoride complex catalyst, which has bad influence on the composition of reaction mixture and restrict its use severely.
Japanese Laid-Open Patent Publication No. 2-45429 discloses a method of carrying out alkylation reaction between olefins and aromatic compounds using a boron trifluoride ether complex, which comprises adding 0.05-2 mol of weak acids such as phosphoric acid, acetic acid and phenol to a boron trifluoride ether complex in the reaction system at room temperature at any stage before or after the reaction, then separating the catalyst by settling in the reaction mixture, and using the separated catalyst as it stands in the next alkylation reaction.
In this case, however, the recovered complex is not an initial boron trifluoride ether complex catalyst, but a boron trifluoride/weak acid complex catalyst in which ether as complexing agent has been replaced with a weak acid added later. Further, the recovery is as low as about 27% by weight.
Olefins having vinylidene structures as double bonds in oligomer are utilized effectively, because they react with maleic acid or else at a high rate. Therefore, several methods have been proposed which introduce much more vinylidene structures into oligomer.
For example, U.S. Pat. No. 4,152,499 discloses a polymerization method in which isobutene is polymerized in the range of temperature from -50.degree. C. to +30.degree. C. to produce polyisobutene having polymerization degree of 10-100 by using a gaseous boron trifluoride catalyst or a boron trifluoride complex catalyst made by complexing with water or alcohol. This method shows that it is possible to introduce 60-90% of vinylidene double bonds at terminal positions.
European Patent 0 145 235 A discloses that polyisobutene is obtained by using a boron trifluoride alcohol complex catalyst comprised of boron trifluoride and C.sub.1 -C.sub.8 alcohols, and describes that it is possible to introduce 70-90% of vinylidene double bonds at terminal positions.
In the production of olefin oligomers as the above, a boron trifluoride complex catalyst is generally used, which has each particular complexing agent selected and its molar coordination number is specified. Thus, ligands bound in a complex demonstrate the desired catalyst functions by specifying the coordination number. Therefore, when a complex catalyst is recovered and reused, it is necessary to recover the complex without any change in coordination number. If the coordination number is varied in recovering, the catalyst function changes, and its readjustment must be carried out after recovering. Therefore, the above recovering method is not preferable.
However, as the coordination number is susceptible to conditions such as temperature and others, the recovering and the reusing of complex catalysts have scarcely been done in the production of olefin oligomer using a boron trifluoride complex catalyst.
The object of the present invention is to provide a method for recovering a boron trifluoride complex as it stands, for example, in the state of maintaining activity of a catalyst, from an electrically-nonconductive fluid containing the complex dispersed and/or dissolved therein, and a process for producing olefin oligomer characterized by recovering and reusing the complex catalyst.